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Java Cookbook
book

Java Cookbook

by Ian F. Darwin
June 2001
Intermediate to advanced content levelIntermediate to advanced
888 pages
21h 1m
English
O'Reilly Media, Inc.
Content preview from Java Cookbook

Storing a Larger Number in a Smaller

Problem

You have a number of a larger type and you want to store it in a variable of a smaller type.

Solution

Cast the number to the smaller type. (A cast is a type listed in parentheses before a value that causes the value to be treated as though it were of the listed type.)

For example, to cast a long to an int, you need a cast. To cast a double to a float, you also need a cast.

Discussion

This causes newcomers some grief, as the default type for a number with a decimal point is double, not float. So code like:

float f = 3.0;

won’t even compile! It’s as if you had written:

double tmp = 3.0; 
float f = tmp;

You can fix it either by making f be a double, by making the 3.0 be a float, by putting in a cast, or by assigning an integer value of 3:

double f = 3.0; 
float f = 3.0f; 
float f = 3f; 
float f = (float)3.0; 
float f = 3;

The same applies when storing an int into a short, char, or byte:

// CastNeeded.java 
public static void main(String argv[]) { 
    int i, k; 
    double j = 2.75; 
    i = j;            // EXPECT COMPILE ERROR 
    i = (int)j;        // with cast; i gets 2 
    System.out.println("i =" + i); 
    byte b; 
    b = i;            // EXPECT COMPILE ERROR 
    b = (byte)i;    // with cast, i gets 2 
    System.out.println("b =" + b); 
}

The lines marked EXPECT COMPILE ERROR will not compile unless either commented out or changed to be correct. The lines marked “with cast” show the correct forms.

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Publisher Resources

ISBN: 0596001703Supplemental ContentCatalog PageErrata